Etching method

ABSTRACT

An etching method of etching a first region including a multilayered film, in which silicon oxide films and silicon nitride films are alternately stacked, and a second region including a single-layered silicon oxide film is provided. The etching method includes a first plasma process of generating plasma of a first processing gas containing a fluorocarbon gas and an oxygen gas within a processing vessel of a plasma processing apparatus; and a second plasma process of generating plasma of a second processing gas containing a hydrogen gas, nitrogen trifluoride gas, a hydrogen bromide gas and a carbon-containing gas within the processing vessel. A temperature of an electrostatic chuck is set to a first temperature in the first plasma process, and the temperature of the electrostatic chuck is set to a second temperature lower than the first temperature in the second plasma process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2015-109568 filed on May 29, 2015, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to an etching method;and, more particularly, to a method of etching a first region includinga multilayered film in which a plurality of silicon oxide films and amultiplicity of silicon nitride films are alternately stacked and asecond region including a single-layered silicon oxide film.

BACKGROUND

As one kind of semiconductor devices, a NAND type flash memory devicehaving a three-dimensional structure is known in the art. In themanufacture of the NAND type flash memory device having thethree-dimensional structure, by performing an etching process of etchinga multilayered film in which silicon oxide films and silicon nitridefilms are alternately stacked on top of each other, a deep hole isformed in the multilayered film. This etching process is described inPatent Document 1.

To be specific, in Patent Document 1, there is disclosed a method ofetching a multilayered film by exposing a processing target objecthaving a mask on the multilayered film to plasma of a processing gas.

Patent Document 1: US Patent Application Publication No. 2013/0059450

A processing target object to be etched may include a first regionincluding a multilayered film in which silicon oxide films and siliconnitride films are alternately stacked on top of each other; and a secondregion including a single-layered silicon oxide film. It is required toform spaces such as a hole and/or a trench in both of the first regionand the second region by etching the processing target object. Further,when performing this etching process, it is also required that a depthof the space formed in the first region and a depth of the space formedin the second region be substantially same, a deformation degree of aplanar shape of the space be small, and, especially, the deformationdegree of the space at a bottom portion (deep portion) thereof be small.Here, the deformation of the space refers to a phenomenon that anactually formed space has a planar shape different from a requiredplanar shape. For example, if the required planar shape is a circularshape, the deformation of space refers to a phenomenon that the actuallyformed space has a planar shape different from the circular shape.

SUMMARY

In one exemplary embodiment, an etching method of etching a first regionand a second region of a processing target object is provided. The firstregion includes a multilayered film in which silicon oxide films andsilicon nitride films are alternately stacked. The second regionincludes a single-layered silicon oxide film. The processing targetobject includes a mask provided with openings on the first region andthe second region. The etching method includes (i) mounting theprocessing target object on an electrostatic chuck provided within aprocessing vessel of a plasma processing apparatus; (ii) generatingplasma of a first processing gas containing a fluorocarbon gas and anoxygen gas within the processing vessel (hereinafter, referred to as“first plasma process”); and (iii) generating plasma of a secondprocessing gas containing a hydrogen gas, a nitrogen trifluoride gas, ahydrogen bromide gas and a carbon-containing gas within the processingvessel (hereinafter, referred to as “second plasma process”). Here, atemperature of the electrostatic chuck is set to a first temperature inthe first plasma process, and the temperature of the electrostatic chuckis set to a second temperature lower than the first temperature in thesecond plasma process.

The etching by the plasma of the first processing gas is characterizedin that an etching rate of the second region is higher than an etchingrate of the first region. Further, in the etching by the plasma of thefirst processing gas, the deformation degree of the formed space at thebottom portion thereof increases. Further, in the etching by the plasmaof the first processing gas, the higher the temperature of theelectrostatic chuck, i.e., the temperature of the processing targetobject becomes, the smaller the deformation degree of the openings ofthe mask becomes, though the etching rate of the first region decreases.

The etching by the plasma of the second processing gas is characterizedin that the etching rate of the first region is higher than the etchingrate of the second region, and the deformation degree of the formedspaces at the bottom portions thereof is small. Further, in the etchingby the plasma of the second processing gas, the lower the temperature ofthe electrostatic chuck, i.e., the temperature of the processing targetobject becomes, the higher the etching rate of the first region becomes.Further, in the etching by the plasma of the second processing gas, whenthe temperature of the electrostatic chuck, i.e., the temperature of theprocessing target object is low, it is possible to suppress occurrenceof a phenomenon that a portion of the space in the depth directionthereof is enlarged in a transverse direction.

Since the etching by the plasma of the first processing gas has theabove-described characteristics, the space formed in the second regionis deeper than the space formed in the first region upon the completionof the first plasma process. Further, the deformation degree of thespaces at the bottom portions thereof is increased. In addition, in thefirst plasma process, since the temperature of the electrostatic chuckis set to the first temperature which is relatively high, the etching bythe plasma of the first processing gas is performed in the state thatthe temperature of the processing target object is set to a relativelyhigher temperature. Accordingly, the deformation degree of the openingsof the mask is decreased after the first plasma process is completed.

The etching by the plasma of the second processing gas has theabove-described characteristics. Accordingly, after the second plasmaprocess is completed, a difference in a depth of the space formed in thefirst region and a depth of the space formed in the second region isreduced or removed. Further, the deformation degree of the spaces at thebottom portions thereof that has occurred in the first plasma process isdecreased. Thus, according to the etching method, the depths of thespaces formed in the first region and the second region becomessubstantially same, and the deformation degree of the spaces at thebottom portions thereof is decreased. Furthermore, in the second plasmaprocess, since the temperature of the electrostatic chuck is set to thesecond temperature which is relatively low, the etching by the plasma ofthe second processing gas is performed in the state that the temperatureof the processing target object is set to a relatively lowertemperature. Accordingly, in the second plasma process, the enlargementof the space in the transverse direction can be suppressed, and theetching rate of the first region is increased.

The first temperature may be in the range from 20° C. to 40° C., and thesecond temperature may be lower than 20° C.

The processing target object may include, as a base of the first regionand the second region, an underlying layer made of silicon or tungsten.Further, the first plasma process and the second plasma process may beperformed until immediately before the underlying layer is exposed. Thatis, the first plasma process and the second plasma process are performedsuch that the first region and the second region are slightly left onthe underlying layer. The method may further include generating plasmaof a third processing gas containing a fluorocarbon gas and an oxygengas within the processing vessel (hereinafter, referred to as “thirdplasma process”). The temperature of the electrostatic chuck is set to athird temperature higher than the first temperature in the third plasmaprocess. The plasma of the third processing gas generated in the thirdplasma process does not substantially etch the underlying layer.Further, in the third plasma process, since the temperature of theelectrostatic chuck is set to the third temperature which is relativelyhigh, the temperature of the processing target object is increased, sothat an adhesion coefficient of active species to the underlying layeris reduced. Therefore, it is possible to suppress damage of theunderlying layer that might be caused by the etching during a period inwhich the underlying layer is exposed. Further, the third temperaturemay be equal to or higher than 70° C.

A sequence including the first plasma process and the second plasmaprocess may be repeated multiple times. According to this exemplaryembodiment, it is possible to etch the first region and the secondregion while reducing the difference in the depths of the spaces formedin the first region and the second region and the difference in thedeformation degree of the spaces.

According to the exemplary embodiments as described above, in thetechnique of etching the first region including the multilayered film,in which silicon oxide films and silicon nitride films are alternatelystacked, and the second region including the single-layered siliconoxide film, it is possible to form spaces in the first region and thesecond region while allowing the spaces formed in the first region andthe second region to have substantially the same depth and, also,allowing the deformation degree of the space at the bottom portionthereof to be small.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described asillustrations only since various changes and modifications will becomeapparent to those skilled in the art from the following detaileddescription. The use of the same reference numbers in different figuresindicates similar or identical items.

FIG. 1 is a flowchart for describing an etching method according to anexemplary embodiment;

FIG. 2 is a cross sectional view illustrating an example of a processingtarget object on which the etching method of FIG. 1 is performed;

FIG. 3 is a diagram schematically illustrating an example of a plasmaprocessing apparatus in which the etching method of FIG. 1 is performed;

FIG. 4 is a cross sectional view illustrating an example state of theprocessing target object in the middle of performing the etching methodof FIG. 1;

FIG. 5 is a cross sectional view illustrating an example state of theprocessing target object in the middle of performing the etching methodof FIG. 1;

FIG. 6 is a cross sectional view illustrating an example state of theprocessing target object after performing the etching method of FIG. 1;

FIG. 7 is a graph showing a result of an experimental example 1;

FIG. 8 is a graph showing a result of an experimental example 2; and

FIG. 9 is a graph showing a result of the experimental example 2.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of the description. In thedrawings, similar symbols typically identify similar components, unlesscontext dictates otherwise. Furthermore, unless otherwise noted, thedescription of each successive drawing may reference features from oneor more of the previous drawings to provide clearer context and a moresubstantive explanation of the current exemplary embodiment. Still, theexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other embodiments may beutilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein and illustrated in the drawings, may bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are explicitlycontemplated herein.

FIG. 1 is a flowchart for describing an etching method according to anexemplary embodiment. The method MT shown in FIG. 1 is directed toforming spaces such as a hole or a trench both on a first region and asecond region of a processing target object (hereinafter, referred to as“wafer”) W by etching the first region and the second region. Thismethod MT is applicable to the manufacture of, for example, a NAND typeflash memory having a three-dimensional structure.

FIG. 2 is a cross sectional view illustrating an example of theprocessing target object on which the etching method of FIG. 1 isperformed. The wafer W shown in FIG. 2 has an underlying layer UL, afirst region R1, a second region R2 and a mask MSK. The underlying layerUL is provided on a substrate. The underlying layer UL is made of, byway of example, but not limitation, silicon or tungsten. As a morespecific example, the underlying layer UL is a polycrystalline siliconlayer.

The first region R1 and the second region R2 are provided on a surfaceof the underlying layer UL. The first region R1 is formed of amultilayered film. The multilayered film includes multiple silicon oxidefilms IL1 and multiple silicon nitride films IL2 which are alternatelystacked on top of each other. A thickness of each of the silicon oxidefilms IL1 is in the range from, e.g., 5 nm to 50 nm, and a thickness ofeach of the silicon nitride films IL2 is in the range from, e.g., 10 nmto 75 nm. According to the exemplary embodiment, the multilayered filmin the first region R1 has twenty-four or more layers in total. Thesecond region R2 is formed of a single-layered silicon oxide film. Athickness of the second region R2 is substantially the same as athickness of the first region R1.

The mask MSK is provided on the first region R1 and the second regionR2. The mask MSK is provided with a pattern for forming spaces such asholes or trenches in the first region R1 and the second region R2. Thatis, the mask MSK is provided with openings OP on the first region R1 andthe second region R2. The mask MSK may be made of, by way ofnon-limiting example, amorphous carbon. Alternatively, the mask MSK maybe made of, for example, organic polymer, poly silicon, or amorphoussilicon.

Referring back to FIG. 1, in the process ST1 of the method MT, the waferW is carried in a processing vessel of a plasma processing apparatus andmounted on an electrostatic chuck of the plasma processing apparatus.FIG. 3 is a diagram schematically illustrating an example of the plasmaprocessing apparatus in which the method shown in FIG. 1 is performed.FIG. 3 illustrates a cross section of the example plasma processingapparatus.

The plasma processing apparatus 10 shown in FIG. 3 is configured as acapacitively coupled plasma etching apparatus and includes asubstantially cylindrical processing vessel 12. The processing vessel 12is formed of, by way of example, but not limitation, aluminum, and aninner wall surface of the processing vessel 12 is anodically oxidized.This processing vessel 12 is frame-grounded.

A supporting member 14 is provided on a bottom portion of the processingvessel 12. The supporting member 14 has a substantially cylindricalshape and is made of an insulating material such as, but not limited to,quartz or alumina. Within the processing vessel 12, the supportingmember 14 is vertically extended from the bottom portion of theprocessing vessel 12. The processing vessel 12 also includes a mountingtable PD, and the mounting table PD is supported on the supportingmember 14.

The mounting table PD includes a lower electrode 16 and an electrostaticchuck 18. The lower electrode 16 includes a first member 16 a and asecond member 16 b. Each of the first member 16 a and the second member16 b is made of a metal such as aluminum and has a substantially diskshape. The second member 16 b is provided on the first member 16 a andis electrically connected to the first member 16 a.

The electrostatic chuck 18 is provided on the lower electrode 16.Specifically, the electrostatic chuck 18 is provided on the secondmember 16 b. The electrostatic chuck 18 is configured to hold the waferW which is placed on a top surface thereof. The electrostatic chuck 18includes a substantially disk-shaped insulating film; and an electrode18 a embedded in the insulating film. The electrode 18 a is connected toa DC power supply 22 via a switch SW. If a DC voltage from the DC powersupply 22 is applied to the electrode 18 a of the electrostatic chuck18, an electrostatic force such as a Coulomb force is generated. Theelectrostatic chuck 18 is configured to attract and hold the wafer W bythe generated electrostatic force.

A focus ring FR is provided on a peripheral portion of the lowerelectrode 16. The focus ring FR has an annular plate shape and isprovided to surround an edge of the wafer W and an edge of theelectrostatic chuck 18. The focus ring FR is made of a material which isappropriately selected based on a material of a target film to beetched. By way of non-limiting example, the focus ring FR may be made ofquartz.

The plasma processing apparatus 10 also includes a temperature controldevice configured to control a temperature of the electrostatic cuck 18.To elaborate, a flow path 16 f for a fluid is provided within the lowerelectrode 16. The flow path 16 f is connected to a pipeline 26 a and apipeline 26 b, and the pipelines 26 a and 26 b are connected to achiller unit CU provided outside the processing vessel 12. A heattransfer medium is supplied into the flow path 16 f from the chillerunit CU via the pipeline 26 a. The heat transfer medium supplied intothe flow path 16 f is returned back into the chiller unit CU via thepipeline 26 b. In this way, the heat transfer medium is circulatedbetween the flow path 16 f and the chiller unit CU. Accordingly, thetemperature of the electrostatic chuck 18 is controlled, so that atemperature of the wafer W is controlled.

Further, the plasma processing apparatus 10 is also equipped with a gassupply line 28 as a part of the temperature control device. A heattransfer gas, for example, a He gas, is supplied from a heat transfergas supply device into a gap between a top surface of the electrostaticchuck 18 and a rear surface of the wafer W. In addition, as a part ofthe temperature control device, a heater 18 h is provided within theelectrostatic chuck 18. The heater 18 h is connected to a heater powersupply HP. Heat is generated from the heater 18 h by a power suppliedfrom the heater power supply HP. Accordingly, the temperature of theelectrostatic chuck 18 is controlled, so that the temperature of thewafer W is also controlled.

Moreover, the plasma processing apparatus 10 further includes the upperelectrode 30. The upper electrode 30 is provided above the mountingtable PD, facing the mounting table PD. A processing space S in which aplasma process is performed on the wafer W is formed between the upperelectrode 30 and the mounting table PD.

The upper electrode 30 is supported at an upper portion of theprocessing vessel 12 with an insulating shield member 32 therebetween.The upper electrode 30 may include a ceiling plate 34 and a supportingbody 36. The ceiling plate 34 directly faces the processing space S andis provided with a multiple number of gas discharge holes 34 a. Theceiling plate 34 may be made of a conductor or a semiconductor havinglow resistance and low Joule heat.

The supporting body 36 is configured to support the ceiling plate 34 ina detachable manner, and is made of a conductive material such as, butnot limited to, aluminum. The supporting body 36 may have awater-cooling structure. A gas diffusion space 36 a is formed within thesupporting body 36. A multiple number of gas through holes 36 b isextended downwards from the gas diffusion space 36 a, and these gasthrough holes 36 b respectively communicate with the gas discharge holes34 a. Further, the supporting body 36 is also provided with a gas inletopening 36 c through which a processing gas is introduced into the gasdiffusion space 36 a, and this gas inlet opening 36 c is connected to agas supply line 38.

The gas supply line 38 is connected to a gas source group 40 via a valvegroup 42 and a flow rate controller group 44. The gas source group 40includes a plurality of gas sources for a first processing gas, a secondprocessing gas and a third processing gas. To elaborate, the gas sourcesmay include one or more gas sources of a fluorocarbon gas, a gas sourceof an oxygen gas (O₂ gas), a gas source of a hydrogen gas (H₂ gas), agas source of a hydrofluorocarbon gas, a gas source of a nitrogentrifluoride gas (NF₃ gas), a gas source of a hydrogen bromide gas (HBrgas), a gas source of a carbon-containing gas, and a gas source of arare gas. As an example, the fluorocarbon gas may contain at least oneof a C₄F₆gas, a C₄F₈ gas and a CF₄ gas. The hydrofluorocarbon gas maybe, by way of example, but not limitation, a CH₂F₂ gas. Thecarbon-containing gas is any gas containing carbon, and, for example,may be a hydrocarbon gas such as a methane gas (CH₄ gas). The rare gasmay be, for example, an Ar gas.

The valve group 42 includes a multiple number of valves, and the flowrate controller group 44 includes a multiple number of flow ratecontrollers such as mass flow controllers (MFC). Each of the gas sourcesbelonging to the gas source group 40 is connected to the gas supply line38 via each corresponding flow rate controller belonging to the flowrate controller group 44 and each corresponding valve belonging to thevalve group 42. In the plasma processing apparatus 10, a gas from a gassource selected from the gas sources is introduced into the processingvessel 12. To be specific, the first processing gas, the secondprocessing gas and the third processing gas are selectively suppliedinto the processing vessel 12. Details of the first processing gas, thesecond processing gas and the third processing gas will be elaboratedlater.

The plasma processing apparatus 10 may further include a groundingconductor 12 a. The grounding conductor 12 a has a substantiallycylindrical shape, and is extended upwards from a sidewall of theprocessing vessel 12 up to a position higher than the upper electrode30.

Further, in the plasma processing apparatus 10, a deposition shield 46is detachably provided along an inner wall of the processing vessel 12.The deposition shield 46 is also provided on an outer side surface ofthe supporting member 14. The deposition shield 46 is configured tosuppress an etching byproduct from adhering to the processing vessel 12,and is formed by coating an aluminum member with ceramics such as Y₂O₃.

A gas exhaust plate 48 is provided between the supporting member 14 andthe inner wall of the processing vessel 12. The gas exhaust plate 48 isprovided with a multiple number of through holes in a plate thicknessdirection thereof. For example, the gas exhaust plate 48 may implementedby an aluminum member coated with ceramics such as Y₂O₃. Further, theprocessing vessel 12 is also provided with a gas exhaust opening 12 eunder the gas exhaust plate 48. The gas exhaust opening 12 e isconnected with a gas exhaust device 50 via a gas exhaust line 52. Thegas exhaust device 50 includes a pressure control valve and a vacuumpump such as a turbo molecular pump, and is capable of decompressing theinside of the processing vessel 12 to a required vacuum level.Furthermore, an opening 12 g through which the wafer W is transferred isformed at a sidewall of the processing vessel 12, and the opening 12 gis opened or closed by a gate valve 54.

Furthermore, a conductive member (GND block) 56 is provided at the innerwall of the processing vessel 12. The conductive member 56 is placed tothe inner wall of the processing vessel 12 such that it is located at aposition substantially level with the wafer W in a height direction. Theconductive member 56 is DC-connected to the ground, and has an effect ofsuppressing an abnormal electric discharge. Further, the arrangementlocation of the conductive member 56 may not be limited to the positionshown in FIG. 3 as long as it is provided within a plasma generationregion.

Further, the plasma processing apparatus 10 further includes a firsthigh frequency power supply 62 and a second high frequency power supply64. The first high frequency power supply 62 is configured to generate afirst high frequency power for plasma generation. The first highfrequency power supply 62 generates the first high frequency powerhaving a frequency ranging from 27 MHz to 100 MHz, for example, 40 MHz.The first high frequency power supply 62 is connected to the lowerelectrode 16 via a matching device 66. The matching device 66 includes acircuit configured to match an output impedance of the first highfrequency power supply 62 and an input impedance at a load side (lowerelectrode 16). Here, the first high frequency power supply 62 may beconnected to the upper electrode 30 via the matching device 66.

The second high frequency power supply 64 is configured to generate asecond high frequency power for attracting ions into the wafer W, i.e.,a high frequency bias power. Specifically, the second high frequencypower supply 64 generates the high frequency bias power having afrequency ranging from 400 kHz to 13.56 MHz, e.g., 3 MHz. The secondhigh frequency power supply 64 is connected to the lower electrode 16via a matching device 68. The matching device 68 includes a circuitconfigured to match an output impedance of the second high frequencypower supply 64 and an input impedance at the load side (lower electrode16).

Further, the plasma processing apparatus 10 further includes a DC powersupply unit 70. The DC power supply unit 70 is connected to the upperelectrode 30. The DC power supply unit 70 is configured to generate anegative DC voltage to apply the DC voltage to the upper electrode 30.

In addition, the plasma processing apparatus 10 further includes acontrol unit Cnt. The control unit Cnt may be implemented by a computerincluding a processor, a storage unit, an input device, a displaydevice, and the like, and is configured to control individual componentsof the plasma processing apparatus 10. Through the control unit Cnt, anoperator can input commands to manage the plasma processing apparatus 10through the input device, and an operational status of the plasmaprocessing apparatus 10 can be visually displayed on the display device.Further, in the storage unit of the control unit Cnt, a control programfor controlling various processes performed in the plasma processingapparatus 10 by the processor, or a program for allowing each componentof the plasma processing apparatus 10 to perform a process according toprocessing conditions, i.e., a process recipe is stored.

In the exemplary embodiment, the control unit Cnt controls, in eachprocess of the method MT, the individual components of the plasmaprocessing apparatus 10 such as the switch SW, the valves of the valvegroup 42, the flow rate controllers of the flow rate controller group44, the gas exhaust device 50, the first high frequency power supply 62,the matching device 66, the second high frequency power supply 64, thematching device 68, the chiller unit CU and the heater power supply HPaccording to the process recipe for the method MT.

Referring back to FIG. 1, the method MT will be further discussed. Inthe following description, FIG. 4 to FIG. 6 as well as FIG. 1 arereferred. FIG. 4 and FIG. 5 are cross sectional views illustrating anexample state of the processing target object in the middle ofperforming the etching method shown in FIG. 1. Further, FIG. 6 is across sectional view illustrating an example state of the processingtarget object after the etching method of FIG. 1 is completed.

As depicted in FIG. 1, in the method MT, the process ST1 is firstperformed as described above. In the process ST1, the wafer W is carriedinto a processing vessel of a plasma processing apparatus and is mountedon a mounting table therein. In case of using the plasma processingapparatus 10, the wafer W is mounted on the electrostatic chuck 18.Then, a voltage from the DC power supply 22 is applied to the electrode18 a of the electrostatic chuck 18, so that the wafer W is attracted andheld by the electrostatic chuck 18.

Thereafter, in the method MT, a process ST2 is performed. In the processST2, plasma of a first processing gas is generated within the processingvessel of the plasma processing apparatus (“first plasma process”). Thefirst processing gas contains one or more kinds of fluorocarbon gasesand an oxygen gas (O₂ gas). In the present exemplary embodiment, thefirst processing gas may contain a C₄F₆gas and a C₄F₈ gas as thefluorocarbon gas. Further, in the present exemplary embodiment, thefirst processing gas may further contain a hydrofluorocarbon gas and/ora rare gas. By way of non-limiting example, a CH₂F₂ gas may be used asthe hydrofluorocarbon gas. As the rare gas, any kind of rare gas can beused. For example, an Ar gas may be used as the rare gas.

In the process ST2, the pressure in the space within the processingvessel is set to have a preset pressure. Further, in the process ST2, atemperature of the electrostatic chuck is set to a first temperature.The first temperature is higher than a second temperature serving as atemperature of the electrostatic chuck which is set in a process ST3 tobe described later. In the exemplary embodiment, the first temperatureis in the range from 20° C. to 40° C. Further, since the wafer Wreceives radiant heat from the plasma, a temperature of the wafer W ishigher than the temperature of the electrostatic chuck by about 10° C.to about 15° C. Accordingly, in the process ST2, the temperature of thewafer W is set to be in the range from 30° C. to 55° C. Further, in theprocess ST2, the first processing gas supplied into the processingvessel is excited, so that the plasma is generated.

In case of using the plasma processing apparatus 10, in the process ST2,the first processing gas is supplied into the processing vessel 12 fromthe gas source selected from the gas sources belonging to the gas sourcegroup 40. Further, a pressure in the space within the processing vessel12 is set to the preset pressure by the gas exhaust device 50. Inaddition, the temperature of the electrostatic chuck 18 is set to thefirst temperature by the chiller unit CU and/or the heater 18 h.Furthermore, the high frequency power from the first high frequencypower supply 62 and the high frequency bias power from the second highfrequency power supply 64 are applied to the lower electrode 16. As aresult, the plasma of the first processing gas is generated within theprocessing vessel 12.

Below, ranges of various conditions in the process ST2 are specified asan example.

Flow rate of C₄F₆ gas: 20 sccm to 100 sccm

Flow rate of C₄F₈ gas: 20 sccm to 100 sccm

Flow rate of CH₂F₂ gas: 20 sccm to 100 sccm

Flow rate of Ar gas: 100 sccm to 500 sccm

Flow rate of oxygen gas: 20 sccm to 200 sccm

Frequency of high frequency power of the first high frequency powersupply 62: 27 MHz to 100 MHz

High frequency power of the first high frequency power supply 62: 100 Wto 5000 W

Frequency of high frequency bias power of the second high frequencypower supply 64: 400 kHz to 3 MHz

High frequency bias power of the second high frequency power supply 64:500 W to 7000 W

Pressure within the processing vessel 12: 2.66 Pa to 13.3 Pa (20 mTorrto 100 mTorr)

Processing time: 180 sec to 600 sec

In the process ST2, as depicted in FIG. 4, a portion of the first regionR1 exposed through an opening OP of the mask MSK is etched, so that aspace SP1 is formed in the first region R1. Further, a portion of thesecond region R2 exposed through an opening OP of the mask MSK isetched, so that a space SP2 is formed in the second region R2. Further,in the etching of the process ST2, a deposit DP is formed on a surfaceof the mask MSK and on wall surfaces of the spaces formed by theetching. The deposit DP is formed of, for example, carbon, fluorocarbonand/or an etching byproduct.

The etching by the plasma of the first processing gas in the process ST2is characterized in that an etching rate of the second region R2 ishigher than an etching rate of the first region R1. Further, in theetching by the plasma of the first processing gas, the deformationdegree of the formed space at a bottom portion (deep portion) thereofincreases. Further, in the etching by the plasma of the first processinggas, the higher the temperature of the electrostatic chuck, i.e., thetemperature of the wafer W becomes, the smaller the deformation degreeof the openings OP of the mask MSK becomes, though the etching rate ofthe first region R1 decreases. Here, the term “deformation” of a spaceor an opening refers to a phenomenon that a planar shape of the space orthe opening on a plane orthogonal to a depth direction thereof becomesdifferent from a required planar shape. For example, in case that therequired planar shape is a circular shape, the deformation of the spaceor the opening refers to a phenomenon that the actually formed space oropening has a planar shape different from the circular shape.

Since the etching by the plasma of the first processing gas has theabove-described characteristics, the space SP2 formed in the secondregion R2 is deeper than the space SP1 formed in the first region R1upon the completion of the process ST2. Further, the deformation degreeof the spaces SP1 and SP2 at the bottom portions thereof is increased.In addition, in the process ST2, since the temperature of theelectrostatic chuck is set to the first temperature which is relativelyhigh, the etching by the plasma of the first processing gas is performedin the state that the temperature of the wafer W is set to a relativelyhigher temperature. Accordingly, the deformation degree of the openingsOP of the mask MSK is decreased after the process ST2 is completed.

Subsequently, in the method MT, a process ST3 is performed. In theprocess ST3, plasma of a second processing gas is generated within theprocessing vessel of the plasma processing apparatus (“second plasmaprocess”). The second processing gas contains a hydrogen gas (H₂ gas), anitrogen trifluoride gas (NF₃ gas), a hydrogen bromide gas (HBr gas) anda carbon-containing gas. The carbon-containing gas contained in thesecond processing gas is any gas containing carbon, and, for example,may be a hydrocarbon gas such as a methane gas (CH₄ gas). In the presentexemplary embodiment, the second processing gas may further contain ahydrofluorocarbon gas and/or a fluorocarbon gas. As an example of thehydrofluorocarbon gas, a CH₂F₂ gas may be used. Further the fluorocarbongas may be, for example, a CF₄ gas.

In the process ST3, the pressure in the space within the processingvessel is set to have a predetermined pressure. Further, in the processST3, the temperature of the electrostatic chuck is set to the secondtemperature. The second temperature is lower than the first temperature.In the present exemplary embodiment, the second temperature is lowerthan 20° C. Further, since the wafer W receives radiant heat from theplasma, the temperature of the wafer W in the process ST3 is set to belower than 30° C. Furthermore, in the process ST3, the second processinggas supplied into the processing vessel is excited, so that the plasmais generated.

In case of using the plasma processing apparatus 10, in the process ST3,the second processing gas is supplied into the processing vessel 12 fromthe gas source selected from the gas sources belonging to the gas sourcegroup 40. Further, the pressure in the space within the processingvessel 12 is set to the predetermined pressure by the gas exhaust device50. In addition, the temperature of the electrostatic chuck 18 is set tothe second temperature by the chiller unit CU and/or the heater 18 h.Furthermore, the high frequency power from the first high frequencypower supply 62 and the high frequency bias power from the second highfrequency power supply 64 are applied to the lower electrode 16. As aresult, the plasma of the second processing gas is generated within theprocessing vessel 12.

Below, ranges of various conditions in the process ST3 are specified asan example.

Flow rate of H₂ gas: 50 sccm to 300 sccm

Flow rate of HBr gas: 5 sccm to 50 sccm

Flow rate of NF₃ gas: 50 sccm to 100 sccm

Flow rate of CH₂F₂ gas: 40 sccm to 80 sccm

Flow rate of CH₄ gas: 5 sccm to 50 sccm

Flow rate of CF₄ gas: 20 sccm to 100 sccm

Frequency of high frequency power of the first high frequency powersupply 62: 27 MHz to 100 MHz

High frequency power of the first high frequency power supply 62: 100 Wto 5000 W

Frequency of high frequency bias power of the second high frequencypower supply 64: 400 kHz to 13.56 MHz

High frequency bias power of the second high frequency power supply 64:1000 W to 7000 W

Pressure within the processing vessel 12: 2.66 Pa to 13.3 Pa (20 mTorrto 100 mTorr)

Processing time: 180 sec to 600 sec

In the process ST3, as depicted in FIG. 5, the portion of the firstregion R1 exposed through the opening OP of the mask MSK is furtheretched, so that the space SP1 is deepened. Further, the portion of thesecond region R2 exposed through the opening OP of the mask MSK isfurther etched, so that the space SP2 is deepened. Further, during theetching of the process ST3, the deposit DP is formed on the surface ofthe mask MSK and on the wall surfaces of the spaces formed by theetching. The deposit DP is formed of, for example, carbon, hydrocarbonand/or an etching byproduct.

The etching by the plasma of the second processing gas in the processST3 is characterized in that the etching rate of the first region R1 ishigher than the etching rate of the second region R2, and thedeformation degree of the formed spaces at the bottom portions thereofis small. Further, in the etching by the plasma of the second processinggas, the lower the temperature of the electrostatic chuck, i.e., thetemperature of the wafer W becomes, the higher the etching rate of thefirst region R1 becomes. Further, in the etching by the plasma of thesecond processing gas, when the temperature of the electrostatic chuck,i.e., the temperature of the wafer W is low, it is possible to suppressoccurrence of a phenomenon that a portion of the space in the depthdirection thereof is enlarged in a transverse direction (orthogonal tothe depth direction of the spaces)

The etching by the plasma of the second processing gas has theabove-described characteristics. Accordingly, after the process ST3 iscompleted, a difference in a depth of the space SP1 formed in the firstregion R1 and a depth of the space SP2 formed in the second region R2 isreduced or removed. Further, the deformation degree of the spaces at thebottom portions thereof that has occurred in the process ST2 isdecreased after the process ST3 is completed. Thus, by performing theprocess ST2 and the process ST3 in sequence, the depths of the spacesformed in the first region R1 and the second region R2 becomessubstantially same, and the deformation degree of the spaces at thebottom portions thereof is decreased. Furthermore, in the process ST3,since the temperature of the electrostatic chuck is set to the secondtemperature which is relatively low, the etching by the plasma of thesecond processing gas is performed in the state that the temperature ofthe wafer W is set to a relatively lower temperature. Accordingly, inthe process ST3, the enlargement of the space in the transversedirection can be suppressed, and the etching rate of the first region R1is increased.

In a subsequent process STJ of the method MT, it is determined whether astop condition is satisfied. Specifically, it is determined that thestop condition is satisfied when a sequence including the process ST2and the process ST3 has been repeated a preset number of times. Thepreset number of times may be one (1) or a plural number. In case thatthe preset number of times is just one, the process STJ is notnecessary. In the present exemplary embodiment where the preset numberof times is set to be the plural number, if it is determined in theprocess STJ that the stop condition is not satisfied, the process ST2and the process ST3 are sequentially performed again. Meanwhile, if itis determined in the process STJ that the stop condition is satisfied,the sequence including the process ST2 and the process ST3 is ended.Further, in the exemplary embodiment where the preset number of times isset to be the plural number, processing times of the process ST2 and theprocess ST3 in each sequence are set to be shorter than processing timesof the process ST2 and the process ST3 in the example where the presetnumber of times is set to be one. As stated above, by performing thesequence including the process ST2 and the process ST3 multiple times,it is possible to etch the first region R1 and the second region R2,while reducing the difference in the depths of the spaces formed in thefirst region R1 and the second region R2 and the deformation degree ofthe spaces.

In the method MT according to the present exemplary embodiment, theprocess ST2 and the process ST3 are performed until immediately beforethe underlying layer UL is exposed. That is, the process ST2 and theprocess ST3 are performed such that the first region R1 and the secondregion R2 are slightly left on the underlying layer. Then, a subsequentprocess ST4 is performed. In the process ST4, plasma of the thirdprocessing gas is generated within the processing vessel of the plasmaprocessing apparatus. As the third processing gas, the same gas as thefirst processing gas may be used.

In the process ST4, the pressure in the space within the processingvessel is regulated to a predetermined pressure. Further, in the processST4, the temperature of the electrostatic chuck is set to a thirdtemperature. The third temperature is higher than the first temperature.In the present exemplary embodiment, the third temperature is set to beequal to or higher than 70° C. Further, since the wafer W receivesradiant heat from the plasma, the temperature of the wafer W is higherthan the temperature of the electrostatic chuck by about 10° C. to about15° C. Accordingly, in the process ST4, the temperature of the wafer Wis set to be equal to or higher than 80° C. Further, in the process ST4,the third processing gas supplied into the processing vessel is excited,so that the plasma is generated.

In case of using the plasma processing apparatus 10, in the process ST4,the third processing gas is supplied into the processing vessel 12 fromthe gas source selected from the gas sources belonging to the gas sourcegroup 40. Further, the pressure in the space within the processingvessel 12 is set to the predetermined pressure by the gas exhaust device50. In addition, the temperature of the electrostatic chuck 18 is set tothe third temperature by the chiller unit CU and/or the heater 18 h.Furthermore, the high frequency power from the first high frequencypower supply 62 and the high frequency bias power from the second highfrequency power supply 64 are applied to the lower electrode 16. As aresult, the plasma of the third processing gas is generated within theprocessing vessel 12.

Below, ranges of various conditions in the process ST4 are specified asan example.

Flow rate of C₄F₆ gas: 20 sccm to 100 sccm

Flow rate of C₄F₈ gas: 20 sccm to 100 sccm

Flow rate of CH₂F₂ gas: 20 sccm to 100 sccm

Flow rate of Ar gas: 100 sccm to 500 sccm

Flow rate of oxygen gas: 20 sccm to 100 sccm

Frequency of high frequency power of the first high frequency powersupply 62: 27 MHz to 100 MHz

High frequency power of the first high frequency power supply 62: 500 Wto 2700 W

Frequency of high frequency bias power of the second high frequencypower supply 64: 400 kHz to 13.56 MHz

High frequency bias power of the second high frequency power supply 64:1000 W to 7000 W

Pressure within the processing vessel 12: 2.66 Pa to 13.3 Pa (20 mTorrto 100 mTorr)

Processing time: 180 sec to 600 sec

In the process ST4, as depicted in FIG. 6, the portions of the firstregion R1 and the second region R2 exposed through the openings OP ofthe mask MSK are further etched, so that the underlying layer UL isexposed via the spaces SP1 and SP2. Further, during the etching of theprocess ST4, the deposit DP is formed on the surface of the mask MSK andon the wall surfaces of the spaces formed by the etching in the samemanner as in the etching of the process ST2.

The plasma of the third processing gas generated in the process ST4 doesnot substantially etch the underlying layer. Further, in the processST4, since the temperature of the electrostatic chuck is set to thethird temperature which is relatively high, the temperature of the waferW is increased, so that an adhesion coefficient of active species to theunderlying layer UL is reduced. Therefore, it is possible to suppressdamage of the underlying layer UL that might be caused by the etchingduring a period in which the underlying layer UL is exposed.

In the above, the method MT according to the exemplary embodiment hasbeen described. However, the above-described exemplary embodiment is notlimiting, and various change and modifications may be made. By way ofexample, the plasma processing apparatus in which the method MT isperformed is not limited to the capacitively coupled plasma processingapparatus, and various other types of plasma processing apparatus suchas an inductively coupled plasma processing apparatus or a plasmaprocessing apparatus with a surface wave such as a microwave as a plasmasource may be used. Further, although the method MT includes the processST4, the underlying layer UL may be exposed by performing the processST2 and the process ST3, and, in such a case, the process ST4 may beomitted.

Hereinafter, experimental examples conducted to evaluate the method MTwill be described. Here, however, it should be noted that theseexperimental examples do not limit the present disclosure.

Experimental Example 1

In the experimental example 1, a plurality of wafers is prepared, andeach of the wafers includes a multilayered film in which multiplesilicon oxide films and multiple silicon nitride films are alternatelystacked on top of each other; and a mask provided with substantiallycircular openings on the multilayered film. Each silicon oxide film hasa thickness of 50 nm, and each silicon nitride film has a thickness of50 nm. The total number of layers of the silicon oxide films is fortyeight (48), and the total number of layers of the silicon nitride filmsis also forty eight (48). The mask is made of amorphous carbon and has afilm thickness of 1500 nm. The opening of the mask has a diameter of 120nm and has a substantially circular planar shape. In the experimentalexample 1, the plasma of the first processing gas is generated in theplasma processing apparatus 10, and the hole is formed in themultilayered film by etching the multilayered film. When etching themultilayered films of the wafers, the temperature of the electrostaticchuck is set to different temperatures for the individual wafers. Below,processing conditions other than the temperature of the electrostaticchuck in the experimental example 1 are specified.

Processing Conditions in Experimental Example 1

Flow rate of C₄F₆ gas: 40 sccm

Flow rate of C₄F₈ gas: 30 sccm

Flow rate of CH₂F₂ gas: 25 sccm

Flow rate of Ar gas: 400 sccm

Flow rate of oxygen gas: 35 sccm

Frequency of high frequency power of the first high frequency powersupply 62: 100 MHz

High frequency power of the first high frequency power supply 62: 1250 W

Frequency of high frequency bias power of the second high frequencypower supply 64: 400 kHz

High frequency bias power of the second high frequency power supply 64:700 W

Pressure within the processing vessel 12: 3.333 Pa (25 mTorr)

Processing time: 600 sec

Then, a SEM image of the opening of the mask and a SEM image of thebottom portion of the hole formed in the multilayered film after theetching of the multilayered film are acquired, and a degree of roundnessof the opening of the mask and a degree of roundness of the hole at thebottom portion thereof are obtained. Further, the etching rate of themultilayered film is also calculated. To obtain the degree of roundnessof the opening of the mask, twenty four (24) line segments that passthrough an approximate center of the opening of the mask and end at anedge of the opening are obtained on the SEM image of the opening, and,among line lengths of the 24 line segments, a minimum line lengthdivided by a maximum line length is calculated as the degree ofroundness of the opening of the mask. Likewise, to calculate the degreeof roundness at the bottom portion of the hole, 24 line segments thatpass through an approximate center of the hole at the bottom portionthereof and end at an edge of the hole at the bottom portion thereof areobtained on the SEM image of the hole, and, among line lengths of the 24line segments, a minimum line length divided by a maximum line length iscalculated as the degree of roundness of the hole at the bottom portionthereof. The degree of roundness of the opening of the mask and thedegree of roundness of the hole at the bottom portion thereof areparameters each of which indicates that the opening or the hole iscloser to a perfect circle as the degree approaches 1.

FIG. 7 is a graph showing the degree of roundness of the opening of themask, the degree of roundness of the hole at the bottom portion thereof,and the etching rate of the multilayered film obtained in theexperimental example 1. In FIG. 7, a horizontal axis indicates thetemperature of the electrostatic chuck when etching the multilayeredfilm; a left vertical axis, the degree of roundness; and a rightvertical axis, the etching rate. As can be seen from FIG. 7, it is foundout that, in the etching by the plasma of the first processing gas, theetching rate of the multilayered film decreases as the temperature ofthe electrostatic chuck increases. Further, it is also found out thatthe degree of roundness of the hole at the bottom portion thereof, whichis formed by the etching with the plasma of the first processing gas, islower than the degree of roundness of a hole at the bottom portionthereof, which is formed by etching with plasma of a second processinggas (refer to a result of an experimental example 2 to be describedlater). That is, it is found out that the deformation degree of thespace at the bottom portion thereof, which is formed by the etching withthe plasma of the first processing gas, is relatively high. Further, itis also found out that, in the etching with the plasma of the firstprocessing gas, the degree of roundness of the opening of the maskincreases as the temperature of the electrostatic chuck increases. Thatis, it is found out that, in the etching by the plasma of the firstprocessing gas, the deformation degree of the opening of the maskdecreases as the temperature of the electrostatic chuck increases.Moreover, it is also found out that the etching rate equal to or higherthan 100 nm/min and the degree of roundness of the opening of the maskequal to or higher than 0.95 can be obtained by setting the temperatureof the electrostatic chuck in the range from 20° C. to 40° C.

Experimental Example 2

In the experimental example 2, a plurality of wafers, which are the sameas the wafers prepared in the experimental example 1, is prepared. Then,the plasma of the second processing gas is generated in the plasmaprocessing apparatus 10, and the hole is formed in the multilayered filmof the wafer W by etching the multilayered film. When etching themultilayered films of the wafers, the temperature of the electrostaticchuck is set to different temperatures for the individual wafers. Below,processing conditions other than the temperature of the electrostaticchuck in the experimental example 2 are specified.

Processing Conditions in Experimental Example 2

Flow rate of H₂ gas: 105 sccm

Flow rate of HBr gas: 40 sccm

Flow rate of NF₃ gas: 70 sccm

Flow rate of CH₂F₂ gas: 65 sccm

Flow rate of CH₄ gas: 35 sccm

Frequency of high frequency power of the first high frequency powersupply 62: 60 MHz

High frequency power of the first high frequency power supply 62: 2500 W

Frequency of high frequency bias power of the second high frequencypower supply 64: 400 kHz

High frequency bias power of the second high frequency power supply 64:4000 W

Pressure within the processing vessel 12: 4 Pa (30 mTorr)

Processing time: 333 sec

Then, a SEM image of an upper portion of the hole formed in themultilayered film, i.e., a SEM image of the hole in the vicinity of aninterface between the multilayered film and the mask is obtained, and aSEM image of a bottom portion of the hole is also acquired. Further, awidth of the hole at the upper portion thereof and a degree of roundnessof the hole at the bottom portion thereof are obtained. Further, anetching rate of the multilayered film is also obtained. The degree ofroundness of the hole at the bottom portion thereof is calculated by thesame method as in the experimental example 1.

FIG. 8 is a graph showing the degree of roundness of the hole at thebottom portion thereof, obtained in the experimental example 2, and FIG.9 is a graph showing the etching rate and the width of the hole at theupper portion thereof, obtained in the experimental example 2. In FIG.8, a horizontal axis indicates the temperature of the electrostaticchuck when etching the multilayered film; a left vertical axis, thewidth of the hole at the upper portion thereof; and a right verticalaxis, the etching rate. As can be seen from FIG. 8, it is found outthat, in the etching by the plasma of the second processing gas, thedegree of roundness of the hole at the bottom portion thereof isimproved regardless of the temperature of the electrostatic chuck. Thatis, it is found out that, in the etching by the plasma of the secondprocessing gas, the deformation degree of the space at the bottomportion thereof, which is formed by the etching, is reduced regardlessof the temperature of the electrostatic chuck. Further, as can be seenfrom FIG. 9, it is also found out that, in the etching by the plasma ofthe second processing gas, the higher etching rate can be obtained asthe temperature of the electrostatic chuck is decreased. In addition, itis also found out that, in the etching by the plasma of the secondprocessing gas, the width of the hole at the upper portion thereofdecreases as the temperature of the electrostatic chuck decreases. Thatis, it is found out that, in the etching by the plasma of the secondprocessing gas, a phenomenon that a portion of the formed space isenlarged in the transverse direction can be effectively suppressed asthe temperature of the electrostatic chuck is decreased. Further, it isalso found out that, in the etching by the plasma of the secondprocessing gas, a sufficiently high etching rate can be obtained and theenlargement of the space in the transverse direction can be sufficientlysuppressed if the temperature of the electrostatic chuck is set to belower than 20° C.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting.

We claim:
 1. An etching method of etching a first region and a secondregion of a processing target object, the first region including amultilayered film in which silicon oxide films and silicon nitride filmsare alternately stacked, the second region including a single-layeredsilicon oxide film, and the processing target object including a maskprovided with openings on the first region and the second region, theetching method comprising: mounting the processing target object on anelectrostatic chuck provided within a processing vessel of a plasmaprocessing apparatus; generating plasma of a first processing gascontaining a fluorocarbon gas and an oxygen gas within the processingvessel; and generating plasma of a second processing gas containing ahydrogen gas, a nitrogen trifluoride gas, a hydrogen bromide gas and acarbon-containing gas within the processing vessel, wherein atemperature of the electrostatic chuck is set to a first temperature inthe generating of the plasma of the first processing gas, and thetemperature of the electrostatic chuck is set to a second temperaturelower than the first temperature in the generating of the plasma of thesecond processing gas.
 2. The etching method of claim 1, wherein thefirst temperature is in the range from 20° C. to 40° C., and the secondtemperature is lower than 20° C.
 3. The etching method of claim 1,wherein the openings are holes.
 4. The etching method of claim 1,further comprising: generating plasma of a third processing gascontaining a fluorocarbon gas and an oxygen gas within the processingvessel, wherein the processing target object includes, as a base of thefirst region and the second region, an underlying layer made of siliconor tungsten, the generating of the plasma of the first processing gasand the generating of the plasma of the second processing gas areperformed until immediately before the underlying layer is exposed, andthe temperature of the electrostatic chuck is set to a third temperaturehigher than the first temperature in the generating of the plasma of thethird processing gas.
 5. The etching method of claim 4, wherein thethird temperature is equal to or higher than 70° C.
 6. The etchingmethod of claim 1, wherein a sequence including the generating of theplasma of the first processing gas and the generating of the plasma ofthe second processing gas is repeated multiple times.